In the reproduction of copies of an original document from video image data created, for example, by electronic input scanning from an original document, it is often desirable to provide functions dependent upon determining the exterior edges of the document. Such features include, for example, automatic magnification, automatic two-up copying, deletion of background image data which falls outside the detected exterior edges of the document, to avoid storing a document requiring more space than necessary, automatic location of the document in a scanning system, electronic deskewing of the electronic image, etc. In other words, to provide these features, the exterior edges of the document must somehow be detected by the scanning system.
Conventionally, to achieve this detection of the exterior edges of the original document, a background has been provided, for the original document, in the scanning system wherein the background provides a backdrop for the original document, such that the background has a tendency to be distinguishable from the original document. For example, backgrounds have been provided with a yellow color, a black color or a white color with a whiter than white color, a backing which fluoresces, and various other alternatives.
Although various alternatives have been utilized, it is most desirable to utilize a dark backing when scanning an original document so as to eliminate show through when scanning a doublesided or watermarked document. Thus, utilizing a light absorbing backing such as a black color, the scanning system can both eliminate show through when scanning the document and enable the scanning system or other downstream image processing system to automatically locate the exterior edges of the original document so that the various features discussed above can be readily implemented.
However, an undesirable consequence of using a light absorbing backing is that any defects in the original document; such as holes, rips, dog-ears, etc. or other characteristic properties of the original; such as pre-punched holes, etc.; appear as black objects when they are rendered and printed on a recording medium. In the following description, the defects in the original and the characteristic properties of the original will be generally referred to as defects; however, this notation does not imply that the physical properties of the original are actual defects, just properties that create artifacts in the scanning process which are undesirable. This problem can be readily seen from the explanation of FIGS. 1 through 6 of the present application as presented below.
FIG. 1 illustrates a conventional platen scanning system wherein an original document 3 has a defect 5 such as a pre-punched hole. In this platen scanning system, an illumination device 9 provides illumination A which passes through platen glass 7 and defect 5, so that it is reflected off of (or absorbed by) backing 2 of a document cover 1 as reflected light B. This reflected light B is sensed by a photoelectric system 11 comprising electronic sensors which convert the light energy into electronic image data. The photoelectric sensor system ("sensors") 11 may be a charged couple device (CCD), a full width array sensor (FWA), or other photoelectric device which can operate in a black/white mode or a color mode.
As further illustrated in FIG. 1, if the illumination source 9 is moved to position C and the sensors 11 are moved to position D, the light generated from the illumination source 9 is reflected back off the document 3 through the platen glass 7 to the sensors 11, so that the sensors 11 can create electric image data which represents an electronic version of the actual image on the document 3.
In another scanning system, a constant velocity transport system (CVT), as illustrated in FIG. 2, a document 3 having a defect 5 is scanned by the scanning system. More specifically, as illustrated in FIG. 2, a light source 9 generates a light A which passes through a small platen glass 70 and further passes through the defect 5 in the document 3. This light is reflected off the roller or ski 13, which supports the document 3 against or in close proximity to the platen glass 70, as reflected light B which is then received by sensor 11. The CVT system further includes guides 17 and 19 (or alternatively a pair of rollers forming a drive nip therebetween) to guide the original document past the scanning station of platen glass 70 and roller or ski 13. The roller or ski 13 is substantially enclosed in a cavity 15 having a particular backing 20.
As the document is moved past the scanning system, as illustrated in FIG. 3, the defect 5 moves outside of the scanning area such that the light A generated from the light source 9 is incident upon the document 3 and the light reflected back as light B to the sensors 11 represents the actual image on document 3.
In all of the above examples, when the conventional scanning system is scanning the area associated with the defect 5, the sensors 11 are in actuality detecting light reflected from the object immediately behind the document; in the platen, the backing of the platen cover, and in the CVT case, the roller or ski 13. However, when the conventional scanning system is scanning a non-defect area of the document 3, the conventional scanning system is receiving light reflected from the actual image on the document 3. In other words, the electronic image data produced from scanning the entire document 3 would include image data representing the area behind the document as well as the image itself.
For example, as shown in FIG. 4, an original document 3 may consist of an image 4 printed on three-hole pre-punched paper such that the three holes are represented by defect 5. If this document is scanned by the conventional CVT system, as illustrated in FIGS. 2 and 3, wherein the objects and devices behind the document, such as a roller or ski 13, and the cavity 15 are non-reflective, the recorded image 40 on a recording medium 30 would also include dark or black regions 50 (scanning artifacts) which correspond to the defects 5 in the original document 3. On the other hand, as illustrated in FIG. 6, if the document of FIG. 4 is scanned by a conventional platen system, as illustrated in FIG. 1, wherein the backing of the platen cover is white, but is dirty from use, has scratches or otherwise is not of a reflectance equivalent to the document background, it is conceivable that the original image region 4 is reproduced as image region 40 on a recording or display medium 30, and that scanning artifacts may still be present in the form of regions 50 corresponding to the defects 5 of the original document 3. If the platen cover backing was non-reflective, the resulting image would be the same as that illustrated in FIG. 5.
Therefore, it is desirable to be able to scan in an original document having certain defects, as described above, and to ultimately render the image on a recording or display medium void of any evidence of the original defects. In other words, the rendered scanning artifacts 50 of FIGS. 5 and 6 would be eliminated, notwithstanding the fact that the original document 3 included defects 5. Moreover, it is desirable to render or display these images without the scanning artifacts and without sacrificing quality or mis-identifying image areas as scanning artifact areas.